Yeah, AFAIK to setup profiles you have to run:

    firefox --ProfileManager

And then to use them you have to start firefox e.g. :

    firefox -P <profile-name>

Very few casual users (nor even most technical users) start Firefox from a command line, and setting up shortcuts for these is also a step that most users won't do.

The support for profiles is there, it's just hard to use in the context of a GUI desktop.